Method of wax removal



2,967,121 METHOD or WAX REMOVAL Joseph C. Allen and Charles C. Nathan,Bellaire, Tern, assignors to Texaco Inc., a corporation of Delaware Thisinvention relates to a method of waxy or parafiinaceous hydrocarbons.More particularly, this invention relates to a method of treating solidwaxy materials to alter their physical properties and/ or appearance.Still more particularly, this invention relates to a method for removingsurface-deposited solid waxy materials.

In accordance With one embodiment the practice of this invention isparticularly suitable for the removal of tenacious, solid waxy materialsand the like from subsurface well equipment, such as pump rods, wellcasing and tubing and the like. The practice of this invention is alsoapplicable for the removal of surface-deposited solid waxy materialsfrom pipe lines, lead lines, tanks and the like employed in orassociated with oil wells and/ or pipe line gathering and transmissionsystems.

In many oil wells and crude oil producing and gathering lines wax orparaflin accumulation is a serious problem. In those wells whereinparaffin deposition is a problem well equipment is regularly treated toremove waxy deposits therefrom. These treatments sometimes involve thecirculation of hot paraflin solvents in contact with the well equipmentfouled by the waxy paraffins in order to dissolve and/or melt away theWaxy materials in contact therewith, or involve the use of mechanicalequipment, such as scrapers or plugs which abrade or Wear away theinterfering, troublesome paraffin or waxy deposits.

It is an object of this invention to provide an improved method for theremoval of waxy deposits from oil well equipment and the like.

Still another object of this invention is to provide a method forreconstituting or otherwise altering the physical properties of waxymaterials, such as are deposited on oil well equipment and petroleumpipe lines and the like during the transportation of waxy hydrocarbonfluids therethrough or in contact therewith.

Still another object of this invention is to provide a method forchanging solid, tenacious, somewhat sticky, waxy hydrocarbons intofinely-crystallized, less tenacious or less sticky waxy hydrocarbons.

How these and other objects of this invention are achieved will becomeapparent in the light of the accompanying disclosure.

In accordance with this invention solid waxy material is subjected tocontact with a gasiform material, such as a gaseous wax solvent orhydrocarbon, which permeates, dissolves or otherwise admixes with saidwaxy material at an elevated pressure, for example, at a pressure of atleast about 1000 p.s.i.g., such as an elevated pressure in the range1500-5000 p.s.i.g. After a period of time sufiicient for the gasiformmaterial to permeate or otherwise enter into or dissolve in the solidwaxy material, the pressure exerted by the gasiform material or gaseoushydrocarbon is rapidly reduced. As a result of the above-indicatedforegoing treatment the solid waxy material is substantially altered,particularly in physical appearance. For example, when a normallygaseous alitreating solid 2,967,121 Patented Jan. 3, 1961 phatichydrocarbon, e.g., methane, ethane, propane and the like, is subjectedto an elevated pressure and maintained in the gaseous form in thepresence of solid waxy materials, the gaseous hydrocarbon, which underan elevated pressure acts as a wax solvent, permeates or dissolves intothe solid waxy material. When the pressure exerted by the gaseoushydrocarbon on the solid Waxy material is suddenly released or otherwiserapidly reduced the solubility of the waxy materials in the pressurizedgaseous hydrocarbon, which has permeated or dissolved into the solidwaxy materials, in elfect, dissolving the solid way materials, issuddenly reduced thereby, in effect, causing a sudden reprecipitation ofthe waxy materials. Due to the sudden reprecipitation the solid waxymaterials are formed into finely divided crystals. These fine crystalstend to be carried away orbe flushed out of the waxy materials by thegaseous bydrocarbon when the ambient pressure is suddenly reduced. Theresulting fine crystalline wax makes up a substantial portion of theresidual wax which is granular and amorphous in appearance. Further, ithas been observed that wax so treated is no longer sticky or tenaciouswhen applied to a ferruginous surface and the like.

Any gaseous wax solvent or gaseous hydrocarbon may be employed in thepractice of this invention. Generally it is desirable to employ anormally gaseous hydrocarbon, such as methane, ethane, propane and thelike, or even ethylene, propylene or acetylene, or mixtures thereof ormixtures containing these normally gaseous hydrocarbons. In the practiceof this invention it is desirable that the pressurized gaseoushydrocarbon and/or wax solvent be maintained .at a temperature above itscritical temperature. Accordingly, it is possible to employ in thepractice of this invention normally liquid aliphatic hydrocarbons, suchas pentanes, hexanes and the like, provided the pressurizing operationis carried out at an elevated temperature above the critical temperatureof the thus-pressurized hydrocarbon. As previously indicated, thepressurized gasiform wax solvent or gaseous hydrocarbon employed in thepractice of this invention may comprise an admixture of normally gaseoushydrocarbons, such as natural gas, methane-propane admixture,methane-butane admixture, methane-isobutane admixture, or an admixtureof a normally gaseous aliphatic hydrocarbon and a normally liquidaliphatic or aromatic hydrocarbon or normally liquid halogenatedhydrocarbons (e.g., halogenated aliphatic hydrocarbons) such asmethane-benzene admixture, methane-toluene admixture, methane-xyleneadmixture, methane-carbon tetrachloride admixture and the like.Desirably an admixture comprising a major amount of methane or ethaneand a minor amount of a material, such as propane, benzene, carbontetrachloride and the like, are employed in the practice of thisinvention.

In accordance with one feature of this inventiondue to the very highpressure required in the practice thereof, retrograde vaporization ofthe normally solid waxy materials into the high pressure phase takesplace. This retrograde vaporization of the normally solid waxyhydrocarbons into the pressurizing gas phase tends to help in theremoval of the waxy solids.

As indicated hereinabove, in the practice of this invention wherein asolid waxy hydrocarbon is in contact with a high pressure gaseoushydrocarbon or wax solvent, such as methane or natural gas or a mixtureof methane and propane or carbon tetrachloride, and the pressure.

suddenly released, evolution of the gaseous hydrocarbon or gasiformmaterials from the solid Waxy material which it has penetrated takesplace. This evolution of the gaseous hydrocarbon causes reprecipitationof any solid waxy material which was solubilized by the gasiforrnmaterial which penetrated the solid waxy material. Also, the evolutionof the gaseous material from the solid waxy material which it hadpenetrated tends to flush outor otherwise mechanically remove ordisplace the resulting recrystallized waxy hydrocarbons. Further, it hasbeen observed that a mechanical disruption of the waxy materials alsotakes place when the ambient pressure, is suddenly released to causerapid evolution of the gaseous material from the wax, thereby in eifectcausing the wax toexplode.

The practice of this invention is more fully set forth in theaccompanying examples wherein experiments were carried out employing aglass-windowed, high pressure test cell. The wax. samples were placed inglass test tubes and the tubes, containing the wax samples placed insidethe pressure cell opposite a glass window. This arrangement permittedvisual observation of the waxy solidmaterials during the-test. Each ofthe tests were carried out at a temperature of about 75 F.

Example I A sample of Texwax, a refined, substantially oil-freepetroleum wax manufactured and sold by The Texas Company, was placed ina test cell and subjected to contact with natural gas at a pressure ofabout 5000 p.s.i.g. After a period of time the pressure within the testcell was rapidly released. It was observed that the wax sample beingtested disintegrated upon sudden pressure reduction and changed from aglossy, crystallineappearing waxy material to a granular, amorphous waxymass.

Example 11 Asample of Texwax, see Example I, was subjected to contactwith a gaseous admixture comprising 86% vol. methane and 14% vol.propane, at a pressure of 5000 p.s.i.g. After a period of time thepressure exerted by the gaseous hydrocarbon mixture on the Wax samplewas reduced as rapidly as possible. When the pressure was reduced on thewax sample, the sample disintegrated to an even higher degree than thatobserved in the test described in Example I.

Example Ill Three dificrent waxes were employed in the following tests,viz., rod and tubing waxes and a refined wax fraction from a Daytoncrude, the refined wax fraction being a high melting, extremely hardwax. In these tests, propane vapor under its own vapor pressure(approximately 130 p.s.i.g.) at room temperature was introduced into thetest cell containing the wax sample. The test cell was connected to anauxiliary test cell which was also filled with propane vapor. With thetwo test cells thus connected, mercury was introduced into the auxiliarycell. As mercury was introducedinto the auxiliary cell; gaseous propanecondensed in each cell. The resulting condensed propane had asolubilizing effect upon each of the wax samples tested. Natural gas wasthen introduced into the test cell and the pressure raised to about 5000p.s.i.g. As the pressure increased the waxy solids appeared to dissolvein the pressurized gas. The gas pressure within the test cell was thenrapidly reduced and gas was observed to be evolved violently from thewaxy admixture in the test cell. When each' of the test wax samples wasremoved from the cell it was found that the wax samples had completelydisintegrated.

Example IV Samples of waxy solids, the same as employed in Example III,were contacted with an admixture ofnatural gas (primarily methane) andcarbon tetrachloride. The gaseous admixture comprising 95% vol. naturalgas and vol. carbon tetrachloride was compressed to about 5000 p.s.i.g.in an auxiliary test cell. The resulting pressurized gaseous admixtureexisted as a single gaseous phase. The single gaseous phase was thenbled into the glass windowed test cell containing the waxy solids to betested. Pressure drop during transfer of the gaseous admixture to thetest cell caused condensation inside the cell and an accumulation ofliquid carbon tetrachloride in the test cell. The test cell pressure wasthen increased by displacing additional gaseous admixture from. theauxiliary cell to the-glass windowed'test cell. At about 3000 p.s.i.g.the liquid in the test tube in the test cell. started to vaporize(retrograde vaporization) and at 4000 p.s.i.g. apparently all of theliquid in the test tube had evaporated. The pressure in the test cellwas then increased to 5000 p.s.i.g. and thereafter released as rapidlyas possible.

Retrograde condensation of carbon tetrachloride oc curred during each ofthe tests. When the test wax' samples were removed from the test cell,the rod and tubing waxes were substantially completely dissolved in thecarbon tetrachloride. Any remaining solid wax was not sticky butappeared mobile with the mixture. The refined wax from the Dayton crudewas about 50% disintegrated.

It was observed prior to the test that the'tubing wax had been found tobe very slowly'soluble in carbon tetrachloride and that during stirringto effect dissolution within carbon tetrachloride the wax tended tostick to the surface of the beaker and stirring rod. It would appear,therefore, in view of the foregoing tests that when carbon tetrachlorideis employed in a high pressure gaseous phase to effect dissolution ofthe waxy materials tested, the gaseous carbon tetrachloride phasepermeates the waxy solids more readily than liquid carbon tetrachloride.

The foregoing experiments indicated the suitability of the practice ofthis invention for cleaning oil well flow strings, pump rods and otheroil well and pipe line equipment with gaseous high pressure solvents ora combination of solvents in admixture with high pressure natural gasand the like. One obvious advantage of the practice of this inventionwould be the elimination of the necessity for pulling rods and/or tubingfor periodic mechanical cleaning to remove the wax therefrom.

As will be apparent to those skilled in the art, many modifications,changes and alterations are possible without departing from the spiritor scope of this invention.

We claim:

1. A method which comprises subjecting solid waxy hydrocarbons tocontact with a normally gaseoushydrocarbon at a temperature above thecritical temperature of said normally gaseous hydrocarbon so that'saidnormally gaseous hydrocarbon remains in the gaseous state, and at anelevated pressure of at least about 1000 p.s.i.g., maintaining said waxyhydrocarbons in contact withthe thus-pressurized normally gaseoushydrocarbon for a period of time sufiicient to permit'said normallygaseous hydrocarbon to permeate said waxy hydrocarbons a substantialextent and to permit atleast a portion of said waxy materials to undergoretrograde vaporization into the thus-pressurized normally gaseoushydrocarbon and subsequently rapidly reducing the pressure exerted bysaid normally gaseous hydrocarbon upon said waxy hydrocarbons.

2. A method in accordance with claim 1 wherein said gaseous hydrocarbonismethane.

3. A method in accordance with gaseous hydrocarbon is ethane.

4. A method in accordance with claim 1 wherein said gaseous hydrocarbonis propane.

claim 1 wherein said Joyce et al.

May 11, 1943 Stewart Nov. 11,1952,

1. A METHOD WHICH COMPRISES SUBJECTING SOLID WAXY HYDROCARBONS TOCONTACT WITH A NORMALLY GASEOUS HYDROCARBON AT A TEMPERATURE ABOVE THECRITICAL TEMPERATURE OF SAID NORMALLY GASEOUS HYDROCARBON SO THAT SAIDNORMALLY GASEOUS HYDROCARBON REMAINS IN THE GASEOUS STATE, AND AT ANELEVATED PRESSURE OF AT LEAST ABOUT 1000 P.S.I.G., MAINTAINING SAID WAXYHYDROCARBONS IN CONTACT WITH THE THUS-PRESSURIZED NORMALLY GASEOUSHYDROCARBON FOR A PERIOD OF TIME SUFFICIENT TO PERMIT SAID NORMALLYGASEOUS HYDROCARBON TO PERMEATE SAID WAXY HYDROCARBONS A SUBSTANTIALEXTENT AND TO PERMIT AT LEAST A PORTION OF SAID WAXY MATERIALS TOUNDERGO RETROGRADE VAPORIZATION INTO THE THUS-PRESSURIZED NORMALLYGASEOUS HYDROCARBON AND SUBSEQUENTLY RAPIDLY REDUCING THE PRESSUREEXERTED BY SAID NORMALLY GASEOUS HYDROCARBON UPON SAID WAXYHYDROCARBONS.